The invention concerns a process for producing platinum alkenyl polysiloxane complex compounds, platinum alkenyl polysiloxane complex compounds produced by this process, especially platinum divinyltetramethyldisiloxane produced by this process, and several uses.
EP 0 979 837 A2 discloses a process for producing a platinum hydrosilylation catalyst, in which a mixture that contains haloplatinic acid, alkenyl polysiloxane, and cycloalkyl polysiloxane is first stirred at a certain temperature, then treated with sufficient alkali to remove essentially the halogen, and then filtered to obtain the corresponding platinum hydrosilylation catalyst, and in which, furthermore, 0.3 to about 20 moles of cycloalkyl polysiloxane must be supplied per mole of alkenyl polysiloxane. In this process, the reaction temperature for the production of the platinum divinylsiloxane hydrosilylation catalyst (Karstedt""s catalyst) is 70xc2x0 C.
The object of the present invention is to provide a process in which the reaction temperature can be kept low, and undesired product impurities can be avoided as far as possible.
In accordance with the invention, this goal is achieved by the process in which a haloplatinum compound is first reacted with at least one alkenyl polysiloxane in the initial presence of platinum in the form of a platinum complex compound as an autocatalyst and in the initial presence of at least one base, especially a bicarbonate, carbonate or hydroxide, at the lowest possible temperature in an organic solvent or mixture of organic solvents that can be oxidized by the haloplatinum compound.
As a rule, the reaction mixture is stirred during the reaction, e.g., by a magnetic stirrer, to provide better mixing and to avoid local overheating. The individual reactants are fed into the reaction mixture, for example, in portions or by drops. The product is recovered by standard methods, say, by separating solid particles from the liquid phase and then concentrating the liquid phase. After the reaction, the customary procedure is to filter the reaction mixture and concentrate the filtrate. The liquid phase contains the reaction product, platinum alkenyl polysiloxane.
Central to the invention is the surprising finding that, when small amounts of platinum alkenyl polysiloxane are present at the start of the reaction, the reaction itself is autocatalyzed, so that the usual reaction temperature can be lowered by as much as 20 K or so, with the result that the actual product is contaminated (with respect to color as well) by fewer decomposition products and by-products. Undesired precipitation of platinum is reduced or entirely suppressed. Furthermore, the lower temperatures provide energy and cost savings.
It is advantageous for platinum in the form of a platinum complex compound to be used as an autocatalyst in an amount of at least 1 wt. %, based on the platinum introduced in the haloplatinum compound.
It is advantageous to add the alkenyl polysiloxane to the solvent or solvent mixture and then to add the haloplatinum compound, since, if they are added in the opposite order, unstable solutions may form, which may continue to react even days after they have been produced.
In the practical application of the process of the invention, divinyltetramethyldisiloxane has been found to be effective as the alkenyl polysiloxane, and hexachloroplatinic (IV) acid has been found to be effective as the haloplatinum compound.
It is also advantageous to wash the filter cake with the solvent or solvent mixture and to combine the second liquid phase obtained in this way with the first liquid phase in order to increase the product yield.
It has been found to be advantageous under practical conditions to use at least one alcohol, especially isopropanol and/or ethanol, as the solvent or solvent mixture.
If the haloplatinum compound is added to the reaction mixture as an anhydrous solution, especially as a solution of the haloplatinum compound in isopropanol, controlled evolution of CO2 gas occurs, which is advantageous, because the gas evolution limits solvent discharge, so that even strict emission limits can be maintained.
It is advisable for the reaction temperature to exceed room temperature, and a reaction temperature above 35xc2x0 C. is advantageous. The reaction with divinyltetramethyldisiloxane can be carried out especially effectively at a temperature of T=+42xc2x0 C. to T=+58xc2x0 C., and a temperature range of T=+48xc2x0 C. to T=+52xc2x0 C. has been found to be especially advantageous in practice. In the case of other siloxanes, the temperature can be from T=+42xc2x0 C. to T=+75xc2x0 C.
Platinum alkenyl polysiloxane produced by this process, especially platinum divinyltetramethyldisiloxane, is not as darkly colored as the substances produced by the prior-art processes and does not tend to produce unwanted precipitation.
A significant factor that contributes to the positive properties is the use of the actual product as an autocatalyst to produce the product, since this makes it possible to lower the reaction temperature by as much as 20 K or so, which in turn results in the formation of fewer decomposition products and by-products and recovery of the reaction product in less contaminated form.
The invention also concerns the use of the platinum alkenyl polysiloxanes that can be produced by the process, namely, both as hydrosilylation catalysts, a use with which the expert is already familiar, and as autocatalysts in the process of the invention.